Nanotechnology involves the synthesis of nanostructures having at least one dimension and a size between 1 and 100 nanometers. These nanostructures are regularly applied in the manufacturing of medical products, drug delivery systems, consumer goods, and miniature electrical components. Carbon nanotubes are of particular interest for the production of nanostructures in that the carbon provides exceptional thermal and electrical conductivity properties allowing their potential use in chemical sensors and catalysts. Some nanotubes have been used in medicine to deliver therapeutic agents to the brain (Oberdorster, et al., 2004) and tumors (Liu et al., 2006. Chakravarty, et al., 2008).
Multi-walled carbon nanotubes (MWCNT) offer excellent potential for industrial and medical uses. Prior to the application of these materials, however, there is a need to improve the understanding of their adverse toxicological effects on workers involved in the production and use of these products. Exposure to nano-sized particles during the manufacture, handling and cleanup of engineered nanomaterials may present extreme hazards to workers depending on the physical and chemical characteristics of the materials that may produce different biological responses than larger materials of the same chemical composition. (Maynard et al., 2004; Oberdorster et al., 2005; Oberdorster, et al, 2005). Low-solubility nanoparticles are more toxic than larger particles of the same material on an equal mass basis (Orberdorster, et al., 2005) illustrating the importance of performing toxicological investigations of manufactured nano-sized particles prior to worker exposure.
Several methods for aerosolizing carbon nanotubes to evaluate their health effects in animals have been described. Mitchell et al. employed a system including a screw feeder, jet mill, and cut-point cyclone to produce a respirable aerosol. (Mitchell et al., 2007) This system produced low concentrations of nanotubes of between 0.1 and 1 mg/m3. The Mitchell method separates fibers by injecting them into a turbulent air stream where they undergo high velocity collisions with other carbon nanotubes similar to the processes used to pulverize materials such as silica. The energy associated with this separation process may alter the physical properties of the aerosolized carbon fibers compared with those found in the air of a carbon nanotube production facility. Care must be taken when extending results generated using this system to actual worker exposure.
A second method employs an ultra high speed knife mill to chop single walled carbon nanotubes to form small particles (Baron et al. 2008). The Baron system produces aerosols that can be used for inhalation studies, although it generates considerable noise that may cause additional stresses to the animals in the exposure chamber. This method also requires continuous adjustments by a well-trained technician.
Due to the importance in obtaining meaningful data relating to the biological effects of MWCNT, and other particulate or molecule containing aerosols, there exists a need for an apparatus and method of delivering highly controlled aerosols of particulate matter for meaningful experimental time periods to an organism.